Geosmin (GM) and 2-methylisoborneol (MIB) are produced by actinomycetes and cyanophytes in the aquatic environment (Gerber 1979; Slater and Block 1983; Persson 1988). These compounds occur in lakes, reservoirs and rivers where GM is more likely to be produced in the water column while MIB is more likely to be produced in sediments (Slater and Blok 1983; Izaguirre et al. 1983). They possess musty, earthy odors at very low thresholds (4 ng/L for GM and 15 ng/L for MIB). Moreover, these compounds tend to accumulate in fish flesh where they can significantly alter its taste and odor. They can also markedly reduce the narcoleptic quality of drinking water (Quatermaine and Anderson 1995). It was recently proposed that zebra mussels indirectly tend to augment the production of these substances because of the accumulation of cyanophytes and actinomycetes in their tissues (Lange and Wittmeyer 1997).